Medicare Parts A Through D Work Together—But Not Always the Way You Think

Key Takeaways

• Medicare Parts A through D are designed to function as a coordinated system, but in practice, they don’t always align seamlessly—gaps, overlapping coverage, and coordination rules can make it confusing.

• Understanding what each part does, when it applies, and where it ends is essential to making Medicare work effectively for your specific healthcare needs in 2025.

What Each Medicare Part Is Supposed to Do

To understand how the system can misalign, you first need to understand how each part is intended to function:

Medicare Part A: Hospital Insurance

Part A is designed to cover:

• Inpatient hospital stays

• Skilled nursing facility care (under specific conditions)

• Hospice care

• Limited home health services

Most people don’t pay a monthly premium for Part A if they’ve worked and paid Medicare taxes for at least 10 years (40 quarters). In 2025, the hospital deductible per benefit period is $1,676.

Medicare Part B: Medical Insurance

Part B covers medically necessary outpatient care, including:

• Doctor visits

• Preventive screenings

• Durable medical equipment

• Mental health outpatient services

In 2025, the monthly Part B premium is $185, with an annual deductible of $257. After the deductible is met, you typically pay 20% of the Medicare-approved amount.

Medicare Part C: Medicare Advantage

Part C isn’t a separate benefit—it’s an alternative to Original Medicare (Parts A and B), offered through private companies approved by Medicare. These plans must cover everything Original Medicare covers and often include additional services like vision, dental, and fitness benefits.

However, how and when you access services can differ from Original Medicare, with network restrictions, prior authorizations, and plan-specific cost structures.

Medicare Part D: Prescription Drug Coverage

Part D helps pay for prescription medications. Plans vary widely, but all must meet standard coverage rules set by Medicare. In 2025, there’s now a $2,000 annual out-of-pocket cap for drug costs, offering financial relief for those with high medication needs.

Where the Coordination Starts—and Stops

While Parts A through D are meant to work together, the actual coordination across them can be limited. Here’s how the integration often breaks down:

1. Gaps Between Part A and Part B

Even though Parts A and B are both part of Original Medicare, they operate under different rules. For instance:

• Part A covers inpatient hospital care, but if you go to the ER and aren’t formally admitted, you could be billed under Part B.

• Skilled nursing facility care requires a qualifying 3-day inpatient hospital stay under Part A—not an observation stay, which would fall under Part B.

2. Part C Replaces A and B—But Not Always Smoothly

When you enroll in a Medicare Advantage plan (Part C), you agree to get your Medicare-covered services through that plan. But that doesn’t mean the transition is seamless:

• Services might require prior approval even if they wouldn’t under Original Medicare.

• You may be limited to a provider network, which can complicate care continuity if your current providers are not in the plan’s network.

• If the plan denies coverage for a service, your appeal rights differ from those under Original Medicare.

3. Part D Stands Alone

Part D is an entirely separate plan that must be selected and maintained independently:

• If you choose Original Medicare, you need to actively enroll in a standalone Part D plan.

• If you enroll in a Medicare Advantage plan that includes drug coverage, you cannot also enroll in a standalone Part D plan.

• Formularies (covered drugs) and tiers vary by plan, and the appeal process for drug coverage decisions can be confusing.

Hidden Gaps You Might Not Notice

Even if you have Parts A through D in place, your coverage may not be as complete as it seems. Here are a few areas where people are often caught off guard:

Long-Term Care Isn’t Covered

Neither Part A nor Part B covers long-term custodial care, such as help with bathing, eating, or dressing. Medicare only covers short-term skilled nursing care under strict conditions. Ongoing long-term care must be paid out-of-pocket or through other means, such as Medicaid or private insurance.

Dental, Vision, and Hearing Can Fall Through the Cracks

Original Medicare does not cover routine dental, vision, or hearing services. Some Medicare Advantage plans offer these benefits, but coverage and access can vary dramatically.

Out-of-Pocket Costs Add Up

Even with all parts in place, you’re still responsible for:

• Deductibles and coinsurance (Parts A and B)

• Premiums (Part B and D, and potentially for Part C)

• Drug costs up to the new $2,000 annual cap (2025)

• Services not covered at all (like overseas care or most dental work)

Coordination Challenges at Key Life Transitions

As your life circumstances change, you might expect Medicare to follow suit. But transitions often introduce new problems:

Turning 65 and First Enrolling

If you enroll in Medicare during your Initial Enrollment Period, you must make several choices:

• Do you stay with Original Medicare and add Part D and a Medigap plan?

• Do you choose a Medicare Advantage plan instead?

Each route affects how your parts interact and what coordination responsibilities fall on you.

Changing Plans During Open Enrollment

Medicare Open Enrollment (October 15 to December 7) allows you to switch plans, but:

• Coverage changes don’t take effect until January 1

• Any disruption in drug coverage (Part D) can have major consequences if not planned properly

Hospital Discharges and Care Planning

When transitioning from hospital to home or a skilled nursing facility, knowing what each part covers is vital:

• Part A may stop paying once you’re discharged, but Part B may or may not pick up depending on services

• Some Medicare Advantage plans have discharge planning services that coordinate better, but not always

When Coordination Works Better

Despite its flaws, there are scenarios where the Medicare system functions more smoothly:

With Medicare Advantage and Part D Bundled

If your Medicare Advantage plan includes drug coverage, the integration is managed by a single provider, which can reduce paperwork and potential coverage gaps. However, this still depends heavily on the plan’s network and benefits.

With Medigap Plans for Original Medicare

A Medigap (Medicare Supplement) policy can fill the cost gaps in Parts A and B, covering things like:

• Coinsurance

• Copayments

• Some deductibles

But even Medigap doesn’t cover drugs (you’ll still need Part D) or services like dental and vision.

Making Medicare Work for You in 2025

Here’s how you can make sure your Medicare coverage is as coordinated as possible this year:

Understand Your Options Before You Enroll

Whether it’s your Initial Enrollment Period, Open Enrollment, or a Special Enrollment Period, take the time to:

• Compare coverage options thoroughly

• Check your doctors and pharmacies for network inclusion

• Review drug formularies to avoid unexpected costs

Stay Aware of Plan Limitations

No plan is perfect. Even with full enrollment in A through D, your:

• Provider access may be restricted

• Drug coverage could change annually

• Cost-sharing responsibilities may increase year to year

Don’t Assume It’s Automatic

Medicare does not automatically coordinate across parts for you. You are responsible for enrolling in the correct combination of parts, reviewing your plan annually, and understanding the terms of your benefits.

Seek Professional Help If Needed

Decisions about Medicare can have long-lasting financial and health impacts. A licensed insurance agent listed on this website can help you understand your choices and enroll in coverage that aligns with your priorities.

Coordinating Your Medicare Coverage Starts With the Right Information

Medicare isn’t a one-size-fits-all program—and the parts that are supposed to work together often leave room for confusion. Whether you’re already enrolled or just getting started, take the time to review how each piece fits into your overall healthcare puzzle. And if you feel uncertain, reach out to a licensed insurance agent listed on this website to guide you through your options.